In typical biological systems, polymerization reactions are driven along a template using a catalyst to specifically read sequence-specific and chain-length-specific information. Typically, the set of structural components that is involved in these in vivo reactions is limited to various combinations using only four base pairs. Additionally, the resulting polymers are typically limited to structures having phosphate-based backbones. Despite these limitations, biological polymers have been able to assemble into phenomenal structures with sophisticated architectures and intricate functions.
An ability to expand the set of structural components would provide almost limitless possibilities for new structures and properties of materials.